A major objective for this year will be to determine the effect of equivalent beta receptor blocking doses of three different beta antagonists, propranolol, sotalol and metoprolol on the dynamic severity of a mechanically-induced fixed coronary artery stenosis in dogs. Blood flow through the stenosis, stenosis resistance, distal bed resistance and tissue blood flow distal to the stenosis will be measured. Preliminary data indicate that beta blockade may reduce the dynamic severity of a fixed proximal coronary stenosis and that this may be a new mechanism by which beta adrenergic blocking agents improve blood flow to ischemic myocardium. We will study the effects of these agents during controlled arterial blood pressure and heart rate to determine the importance of these factors in their beneficial actions. Vagal stimulation will also be investigated as another means of producing hemodynamic effects similar to those observed following beta receptor blockade.